|Series|Year|Rank|Average audience share|
|---|---|---|---|
|1|1992|Unknown|14.50m|
|2|1993|Unknown|Unknown|
|3|1993|Unknown|Unknown|
|4|1994|Unknown|Unknown|
|5|1995|Unknown|Unknown|
|6|1996|Unknown|14.60m|
|7|1997–1998|Unknown|15.82m|
|8|1998–1999|5th|14.35m|
|9|1999–2000|6th|13.71m|
|10|2000–2001|5th|13.21m|
|11|2001–2002|6th|10.77m|
|12|2002–2003|7th|11.29m|
|13|2003–2004|8th|13.11m|
|14|2004–2005|10th|8.77m|
|15|2005–2006|10th|8.42m|
|16|2006–2007|8th|7.80m|
|17|2007–2008|11th|6.90m|
|18|2008–2010|15th|5.44m (Incl. ITV HD)|

Question: how many years did heartbeat series run in total?
Answer: 18